into the sea between Ballard Down, near Poole, on the west, and Calshot Castle and the Medina on the east, but not including the latter river, I find that, according to the Ordnance Map,[1] the present land area which would have drained into an ancient river such as that supposed, is 1,617 square miles. To this may be added another 100 square miles, representing the area included between the present coast and an extension of the chalk downs from Ballard Down to the Needles, the whole of which has been washed away; though within this large area, the present depth of the sea attains in but very few places to ten fathoms. The drainage area of the ancient river Solent can therefore have been but about one-third of that of the Thames and its affluents, unless we are to suppose that, as is the case in the neighbourhood of Carisbrooke Castle and with the Medina, a portion of land to the south of the old chalk downs drained northward through some gap in the range of hills. That such land existed seems probable, from the occurrence of gravels with elephant remains along the south-west coast of the Isle of Wight at an elevation of 80 feet and upwards above the sea, which, Mr. Codrington has suggested, may have been deposited by tributary streams of a river flowing northwards through the chalk range to the Solent. But even with any such addition the area drained by the old River Solent can hardly have been half that of the basin of the Thames.
With regard, however, to the former existence of this range of chalk hills and the land to the north of them, Mr. Codrington has shown, in the paper already so often quoted, that the spreading out of the marine gravel, and the levelling of the table-lands was probably effected in an inlet of the sea, shut in on the southern side by land which connected the Isle of Wight with the mainland, and opening to the eastward. Assuming, then, the existence of this ridge of high land, it is evident, as Mr. Fox has pointed out, that the only outlet for the rivers now represented by the Frome, the Trent or Piddle, the Stour, Blackwater, Avon, and other streams now discharging into the sea, must have been by an eastward channel, in fact, a continuation of the rivers now discharging through Poole Harbour. The course of such a river would naturally be guided, in the first instance, by the configuration of the surface of the old marine gravels of the sloping tableland. This, as has been shown, slopes upward from the present coast northward, and attains its highest level inland; but traces of the same gravel occur also in the Isle of Wight, though it there
- ↑ "Rivers and their Catchment Basins."
